1. Field
The present disclosure relates to random diene copolymers comprising silicon atoms within the main polymer chain. More particularly, the present disclosure relates to the production of these copolymers.
2. Description of Related Art
U.S. Pat. No. 5,357,019 describes the synthesis of crosslinkable polycarbosilanes by reaction of butadiene with a dichlorosilane derivative in the presence of magnesium and iodine in THF. The resulting copolymer alternates the unsaturated units resulting from the diene monomer and the silicon hydride units. In addition, the polymerization times of between 12 h and 24 h are lengthy in order to obtain unsaturated polycarbosilanes having low molecular weights of between 1000 and 20 000 g/mol and high polydispersities.
U.S. Pat. No. 5,171,810 and also the publications of the same authors (Weber et al., Macromolecules, 1988, 21, 1563-1566; Macromolecules, 1990, 23, 1583-1586; Macromolecules, 1990, 23, 1915-1917) for their part relate to the polymerization of unsaturated cyclic carbosilanes by ring opening anionic polymerization, resulting in crosslinkable polycarbosilanes consisting of a perfect alternation of unsaturations and dialkylsilane groups. The resulting homopolymers and copolymers result solely from monomers derived from silacyclopentene, the weight-average molecular weights not exceeding 60 000 g/mol with polydispersities ranging up to 2.6. In addition, this process requires an additional stage of preparation of the silacyclopentene cyclic monomers consisting in reacting butadiene or isoprene with a dichlorosilane derivative in the presence of a metal, such as magnesium or sodium, in a polar solvent, such as THF, diethyl ether or hexamethylphosphoramide (J. Org. Chem., 1968, 33, 1975; J. Organometal. Chem., 1971, 30, 5; J. Organometal. Chem., 1970, 25, 51). The low synthetic yields are between 20% and 40%.
The introduction of unsaturations into polymers of polycarbosilane type has also been carried out during studies on the polymerization by acyclic diene metathesis (ADMET) (Wagener et al., Macromolecules, 1991, 24, 6073-6078). However, the catalysts used require preliminary syntheses and are extremely sensitive to air and to impurities. In addition, their lack of thermostability limits the degree of polymerization for certain monomers. For their part, the various monomers require a synthesis by Grignard route, hydrosilylation or condensation of a silanol and of a chlorosilane.
On the other hand, the groups of M. Gauthier and J. Roovers have described the preparation of hybrid materials based on a polybutadiene shell and a carbosilane dendrimer core by the convergent route (Macromolecules, 2010, 43, 3672; Macromolecules, 1993, 26, 4234). This preparation process consists in synthesizing, in a first step, a carbosilane dendrimer carrying, at the periphery, 32, 64 or 128 reactive chlorosilane functional groups. In a second step, living anionic polybutadienyllithium chains are coupled to these chlorosilane functional groups to generate a hybrid material based on an inorganic carbosilane core and an organopolybutadiene shell.
For its part, the group of M. Moller has presented the synthesis of hybrid materials based on a polybutadiene shell and on a carbosilane dendrimer core by the divergent route (Macromol. Chem. Phys., 1998, 199, 889). The method of preparation consists, in a first step, in synthesizing, by a sequence of stages of hydrosilylation and of reaction with an organomagnesium compound, a polycarbosilane dendrimer carrying unsaturations at the periphery. In a second step, the shell of diene polymers is prepared by living anionic chain growth starting from the lithiated entities generated by reaction of butyllithium with the unsaturations at the periphery. These synthetic strategies have made possible the preparation of polybutadiene stars, for example having 8 or 16 branches.
Patent SU 304 834 describes preparations of copolymers of butadiene and of substituted silacyclobutane in hexane as sole solvent. This patent describes in particular obtaining a copolymer from a specific carbosilane monomer: 1-(p-dimethylaminophenyl)-1-methyl-1-silacyclobutane.
The technical problem which is posed with respect to the state of the art is that of being able to carry out the synthesis of a diene copolymer exhibiting, within the main chain, randomly distributed silicon atoms. More particularly, it is advisable to be able to carry out such a synthesis according to a process which is simple, reproducible, capable of being used on an industrial scale and not exhibiting the disadvantages of the processes of the prior art. In particular, it is advisable to provide a process which does not require the synthesis of the monomers and catalysts, which does not employ long polymerization times and which makes it possible to obtain high molecular weights and low polydispersities.